1. Field of the Invention
The present invention relates to a technique of adjusting the input-output characteristics of an image display apparatus.
2. Description of the Related Art
An image display apparatus like a projector has a signal adjustment device, which adjusts a tone characteristic of an input video signal, in order to correct a non-linear input-output characteristic of the image display apparatus due to a non-linear input-output characteristic (V-T characteristic) of an image display device, such as a liquid crystal panel. The signal adjustment device adjusts the tone characteristic of the input video signal and the input-output characteristic of the image display apparatus, thus attaining adjustment of the contrast, the brightness, and the color tone of a resulting displayed image. The signal adjustment device utilizes three lookup tables to adjust the input-output characteristic of the image display apparatus. Each of the three lookup tables has information representing a mapping of a linear tone value of each color video signal, red (R), green (G), or blue (B) to a tone value corresponding to the adjusted input-output characteristic of the image display apparatus.
A controller connecting with three RAMs writes the information representing the mapping into the three lookup tables.
Each lookup table outputs a color video signal having a tone value corresponding to the tone value of the color video signal input as an address signal of the RAM during a normal image display operation.
In order to adjust the input-output characteristic of the image display apparatus with a high accuracy and attain a high-quality resulting image, it is preferable that the color video signal used as the address signal in each lookup table and the corresponding output color video signal have a greater number of tones. The lookup table thus tends to extend the data width from the conventional 8-bit data to 10-bit data.
The greater input-output data width of the lookup table, however, enhances the quantity of information (quantity of data) included in the lookup table and undesirably lengthens the processing time required for updating and modifying the lookup table. Especially in the case where multiple different processes of adjustment are carried out with regard to the input-output characteristic of the image display apparatus, the information of the lookup table should be computed based on respective pieces of adjustment information. This further increases the processing time required for updating and modifying the lookup table.
The user may desire to change the contrast, the brightness, or the color of the image in the process of displaying the image. In such cases, the lookup tables of the respective colors should be modified. When the lookup table stores the large quantity of information, the processing time required for modifying the lookup tables is undesirably lengthened.